I actually used this as a supplement to Modern Information Retrieval (http://www.amazon.com/Modern-Information-Retrieval-Concepts-...) for my IR class this semester. I found the Stanford book to be much more detailed in terms of the mathematical formalities behind the models/concepts and ended up preferring it.

I can second the recommendation of that book, I've heard a lot of good things, though I haven't read it. It's recently been updated in a 2nd edition [1], though I have no idea if there are substantive changes, presumably, there are, given more than a decade has elapsed. If anyone's read the updated version, I'd appreciate knowing if and/or how the book's changed, I've been thinking about picking it up.

I have read pretty big sections of Manning's Introduction to IR, and it served me fairly well as an introduction to the field. It's available online.[2]

[1] http://www.amazon.com/Modern-Information-Retrieval-Concepts-...

[2] http://nlp.stanford.edu/IR-book/information-retrieval-book.h...